Are you getting regular blood tests like a CBC? If so, you should already have an idea if it's affecting your liver or white blood cells. The Prometheus test won't do that.
You should also consider that your insurance company might not pay for a second Prometheus, and they're on the expensive side.
Why can't you increase the dose by 25 mg every month and follow up with general blood work more frequently, like every two weeks? If your symptoms improve and your labs are fine, I can't see why your doc would object to that strategy, which follows protocols outlined in lit reviews.